The treatment of proliferative disease, particularly cancer, by chemotherapeutic means often relies upon exploiting differences in target proliferating cells and other normal cells in the human or animal body. For example, many chemical agents are designed to be taken up by rapidly replicating DNA so that the process of DNA replication and cell division is disrupted. Another approach is to identify antigens on the surface of tumor cells or other abnormal cells which are not normally expressed in developed human tissue, such as tumor antigens or embryonic antigens. Such antigens can be targeted with binding proteins such as antibodies which can block or neutralize the antigen. In addition, the binding proteins, including antibodies and fragments thereof, may deliver a toxic agent or other substance which is capable of directly or indirectly activating a toxic agent at the site of a tumor.
The EGFR is an attractive target for tumor-targeted antibody therapy because it is overexpressed in many types of epithelial tumors (Voldborg, B. R., et al. (1997) Ann Oncol 8:1197-206; den Eynde, B. and Scott, A. M. (1998) Tumor Antigens. In: P. J. Delves and I. M. Roitt (eds.), Encyclopedia of Immunology, Second Edition, pp. 2424-31. London: Academic Press). Moreover, expression of the EGFR is associated with poor prognosis in a number of tumor types including stomach, colon, urinary bladder, breast, prostate, endometrium, kidney and brain (e.g., glioma). Consequently, a number of EGFR antibodies have been reported in the literature with several undergoing clinical evaluation (Baselga, J., et al. (2000) J Clin Oncol. 18: 904; Faillot, T., et al. (1996) Neurosurgery 39: 478-83; Seymour, L. (1999) Cancer Treat Rev 25: 301-12). Results from studies using EGFR mAbs in patients with head and neck cancer, squamous cell lung cancer, brain gliomas and malignant astrocytomas have been encouraging. The anti-tumor activity of most EGFR antibodies is enhanced by their ability to block ligand binding (Sturgis, E. M., et al. (1994) Otolaryngol Head Neck Surg 111: 633-43; Goldstein, N. I., et al. (1995) Clin Cancer Res 1: 1311-8). Such antibodies may mediate their efficacy through both modulation of cellular proliferation and antibody dependent immune functions (e.g. complement activation). The use of these antibodies, however, may be limited by uptake in organs that have high endogenous levels of EGFR such as the liver and skin (Baselga, J., et al. (2000) J Clin Oncol. 18: 904; Faillot, T., et al. (1996) Neurosurgery 39: 478-83).
A significant proportion of tumors containing amplifications of the EGFR gene (i.e., multiple copies of the EGFR gene) also co-express a truncated version of the receptor (Wikstrand, C. J., et al. (1998) J Neurovirol 4: 148-58) known as de2-7 EGFR, ΔEGFR, or Δ2-7 (terms used interchangeably herein) (Olapade-Olaopa, E. O., et al. (2000) Br J Cancer 82: 186-94). The rearrangement seen in the de2-7 EGFR results in an in-frame mature mRNA lacking 801 nucleotides spanning exons 2-7 (Wong, A. J., et al. (1992) Proc Natl Acad Sci USA 89: 2965-9; Yamazaki, H., et al. (1990) Jpn J Cancer Res 81: 773-9; Yamazaki, H., et al. (1998) Mol Cell Biol 8: 1816-20; Sugawa, N., et al. (1990) Proc Natl Acad Sci USA 87: 8602-6). The corresponding EGFR protein has a 267 amino acid deletion comprising residues 6-273 of the extracellular domain and a novel glycine residue at the fusion junction (Sugawa, N., et al. (1990) Proc Natl Acad Sci USA 87: 8602-6). This deletion, together with the insertion of a glycine residue, produces a unique junctional peptide at the deletion interface. The de2-7 EGFR has been reported in a number of tumor types including glioma, breast, lung, ovarian and prostate (Wikstrand, C. J., et al. (1997) Cancer Res. 57: 4130-40; Olapade-Olaopa, E. O., et al. (2000) Br J Cancer 82: 186-94; Wikstrand, C. J., et al. (1995) Cancer Res 55: 3140-8; Garcia de Palazzo, I. E., et al. (1993) Cancer Res 53: 3217-20). While this truncated receptor does not bind ligand, it possesses low constitutive activity and imparts a significant growth advantage to glioma cells grown as tumor xenografts in nude mice (Nishikawa, R., et al. (1994) Proc Natl Acad Sci USA 91: 7727-31, 1994) and is able to transform NIH3T3 cells and MCF-7 cells (Batra, S. K., et al. (1995) Cell Growth Differ 6: 1251-9). The cellular mechanisms utilized by the de2-7 EGFR in glioma cells are not fully defined but are reported to include a decrease in apoptosis and a small enhancement of proliferation (Nagane, M., et al. (1996) Cancer Res 56: 5079-86).
As expression of this truncated receptor is restricted to tumor cells it represents a highly specific target for antibody therapy. Accordingly, a number of laboratories have reported the generation of both polyclonal and monoclonal antibodies specific to the unique peptide of de2-7 EGFR (Wikstrand, C. J., et al (1998) J Neurovirol 4: 148-58; Humphrey, P. A., et al (1990) Proc Natl Acad Sci USA 87: 4207-11; Okamoto, S., et al (1996) Br J Cancer 73: 1366-72; Hills, D., et al (1995) Int J Cancer 63: 537-43). A series of mouse mAbs, isolated following immunization with the unique de2-7 peptide, all showed selectivity and specificity for the truncated receptor and targeted de2-7 EGFR positive xenografts grown in nude mice (Wikstrand, C. J., et al (1995) Cancer Res 55: 3140-8; Reist, C. J., et al (1997) Cancer Res 57: 1510-5; Reist, C. J., et al (1995) Cancer Res 55: 4375-82).
However, one potential shortcoming of de2-7 EGFR antibodies is that only a proportion of tumors exhibiting amplification of the EGFR gene also express the de 2-7 EGFR. Therefore, de2-7 EGFR specific antibodies would be expected to be useful in only a percentage of EGFR positive tumors. Thus, while the extant evidence of activity of EGFR antibodies is encouraging, the observed limitations on range of applicability and efficacy reflected above remain. Accordingly, it would be desirable to have antibodies and like agents that demonstrate efficacy with a broad range of tumors, and it is toward the achievement of that objective that the present invention is directed. In addition, antibodies which do not target normal tissues and EGFR in the absence of amplification, overexpression, or mutation, would be particularly useful. One such antibody, monoclonal antibody mAb806, has been previously described in WO02092771 and WO05081854. Additional such antibodies are needed and would be desirable.
The citation of references herein shall not be construed as an admission that such is prior art to the present invention.